Nitrite Reduction Research Articles

Phylogenetics and environmental distribution of nitric oxide-forming nitrite reductases reveal their distinct functional and ecological roles.

The two evolutionarily unrelated nitric oxide-producing nitrite reductases, NirK and NirS, are best known for their redundant role in denitrification. They are also often found in organisms that do not perform denitrification. To assess the functional roles of the two enzymes and to address the sequence and structural variation within each, we reconstructed robust phylogenies of both proteins with sequences recovered from 6973 isolate and metagenome-assembled genomes and identified 32 well-supported clades of structurally distinct protein lineages. We then inferred the potential niche of each clade by considering other functional genes of the organisms carrying them as well as the relative abundances of each nir gene in 4082 environmental metagenomes across diverse aquatic, terrestrial, host-associated, and engineered biomes. We demonstrate that Nir phylogenies recapitulate ecology distinctly from the corresponding organismal phylogeny. While some clades of the nitrite reductase were equally prevalent across biomes, others had more restricted ranges. Nitrifiers make up a sizeable proportion of the nitrite-reducing community, especially for NirK in marine waters and dry soils. Furthermore, the two reductases showed distinct associations with genes involved in oxidizing and reducing other compounds, indicating that the NirS and NirK activities may be linked to different elemental cycles. Accordingly, the relative abundance and diversity of NirS versus NirK vary between biomes. Our results show the divergent ecological roles NirK and NirS-encoding organisms may play in the environment and provide a phylogenetic framework to distinguish the traits associated with organisms encoding the different lineages of nitrite reductases.

Introduction of soybean into maize field reduces N2O emission intensity via optimizing nitrogen source utilization

The application of synthetic nitrogen (N) fertilizer has increased anthropogenic N2O emission in global croplands. Due to the advantage of biological nitrogen fixation (BNF), the introduction of legume may lessen N2O emission intensity (emission/yield) in cereal field. Yet, this speculation lacks strong evidences and the relevant mechanistic explanations. A two-year field study was conducted using static chamber method (15N isotope labeling in fertilizer) in the mono- and inter-cropping fields with soybean introduced in maize field in semiarid rainfed Loess Plateau. The results indicated that maize-soybean intercropping showed 13 % lower N2O emission intensity than monocropping, attributed to 14 % and 20 % lower annually N2O emissions in intercropped zone than that of sole maize and soybean zones respectively. Also, a 15 % higher grain yield was observed in intercropped maize relative to that in sole maize. Particularly, during the peak time of emission following N fertilization and BNF within growing season, soybean introduction reduced 25 % and 24 % of N2O emissions in intercropped zone than sole maize and soybean zone respectively. It also favored maize plant with an additional 17 % more fertilizer-derived N, 21 % less soil-derived N and 30 kg N ha−1 soybean transferred-N from BNF. The contributions of N fertilization, BNF and soil initial organic N to N2O production were lessened in intercropping. In this case, the capacity of substrates N transformation into N2O emissions was lowered. Critically, soybean introduction reduced soil ammonia oxidation (as evidenced from amoA AOA and AOB gene abundance) in intercrops’ rhizosphere, and increased soil nitrite reduction (nirS and nirK gene abundance) in maize rhizosphere, and improved soil N2O reduction to N2 (nosZ gene abundance) in soybean rhizosphere. Therefore, soybean introduction optimized N source use for lower N2O emission intensity, via reducing the transformation of substrate N into N2O, and modifying the expression of nitrification and denitrification functional genes.

Isotopic and geochemical modeling approach to evaluate abiotic nitrite reduction by ferrous iron

Nitrite reduction has often been treated as a biotic process in water treatment systems, but it also occurs abiotically, and it is difficult to distinguish both reactions as they can co-occur at field-scale. The potential reduction of NO2− was tested in 3 anaerobic experimental scenarios using a NO2− bearing solution amended with: i) siderite (FeCO3) (Sid experiment); ii) Fe(II) solution from FeCl2.4H2O(s) (DFe experiment); and iii) siderite mixed with Fe(II) solution (Sid+DFe experiment). Non-sterilized batch experiments were carried out in anaerobic conditions with an initial ratio of nitrogen to dissolved iron of 5 in DFe and Sid+DFe (Sid had no initially dissolved Fe(II)) and 1000 mg L−1 of siderite in Sid and Sid+DFe experiments. At the end of the experiments, the NO2− removed was 3% for Sid, 54% for DFe and 84% for Sid+DFe. The NO2− concentration decrease over time was characterized by an enrichment in the δ15NNO2 of the unreacted NO2−, increasing from −26.9 ‰ to −26.4 ‰ (Sid), −18.0 ‰ (DFe) and −15.9 ‰ (Sid+DFe). The calculated ε15NNO2 for Sid was −11.8 ‰, whereas for DFe was −12.0 ‰ and Sid+DFe was −13.0 ‰, suggesting a common NO2− degradation mechanism in all experiments. The Rayleigh distillation equation showed that the generated N2O was the final product of the abiotic nitrite reduction reaction, and the calculated N2O site preference (SP) was 22.5 ± 0.7 ‰ for DFe and 23.5 ± 0.5 ‰ for Sid+DFe. The continuous N2O measurement showed that only 25.3 ± 5.1% in DFe and 31.0 ± 6.3% in Sid+DFe of the generated N2O in water was recovered in the headspace vials, suggesting that a large portion of the produced N2O(aq) in solution did not diffuse from water. The coupled NO2− reduction and Fe(II) oxidation followed a second-order kinetic reaction with a rate equal to (9.39 ± 0.36)·10−4·[NO2−]·[Fe(II)] (mol L−1 s−1) in all experiments. The experimental conditions supported by the Rayleigh distillation equation using the experimentally calculated ε15N values, coupled with NO2− isotopic data and N2O SP values, showed that biological denitrification had a negligible influence on nitrite reduction and that chemodenitrification was the main NO2− attenuation pathway. A geochemical model coupling the kinetic chemodenitrification, isotope fractionation, aqueous speciation in equilibrium and precipitation and dissolution of calcite has been implemented and reproduced the experimental results. The geochemical model developed in our study can be applied to similar experimental studies and to field-scale studies to predict the efficiency of abiotic nitrite reduction treatments using Fe(II).

Synergistically enhancing nitrate reduction into N2 in water by N-doped Pd–Cu biochar bimetallic single-atom electrocatalysis

Noble metal materials have been identified as high efficiency catalysts for electrocatalytic reduction of nitrate, and the synthesis and manufacture of high catalytic activity and environmentally friendly catalysts of activating hydrogen for water purification applications is extremely attractive. In this work, the Pd–Cu single-atom catalysts (Pd–Cu-N-BC) were first prepared by direct growth of Pd–Cu single-atom on bamboo biochar by regulating the concentration of precursors and doping method, and then enhanced electrocatalytic reduction nitrate performance and N2 generation. The results showed that Pd–Cu-N-BC displayed excellent catalytic activity and reusability in electrocatalytic reduction nitrate with a low potential of 0.47 V vs. RHE (@10 mA cm−2). The maximum nitrate removal efficiency and N2 generation could reach about 100% and 72.32% within 180 min, respectively. The density functional theory (DFT) calculations confirmed that Cu atoms could catalyze the electrochemical reduction of nitrate to nitrite, and Pd atoms anchored in the nitrogen-doped biochar (N-BC) lattice could catalyze electrochemical reduction of nitrite to N2 involving the formation of hydrogen radical (H*). The characterization results of XANES showed that electronic synergistic effect between Pd and Cu single atoms significantly promotes the N2 production through hydrogenation while inhibiting the generation of byproducts, leading to significantly enhanced electrocatalytic reduction of nitrate to N2. Finally, Pd–Cu-N-BC was designed as a 3D particle electrode for enhanced electrocatalytic reduction of nitrate, exhibiting excellent stability and reusability, which could be considered as a suitable candidate for applications in the remediation of nitrate contamination.Graphical

Electrocatalytic Nitrite Reduction in Neutral Water with Ni(II) and Co(II) Macrocycle Complexes: Catalytic Evaluation and Mechanistic Elucidation

AbstractNitrite anions, of anthropogenic origin, in the environment disrupt the nitrogen cycle making the electrocatalytic reduction of nitrite a significant objective. Homogeneous Ni(II) and Co(II) complexes bearing a macrocyclic supporting ligand consisting of a tridentate redox active bis(imino)pyridine moiety coupled with a tertiary amine donor site are effective and selective for the electrocatalytic reduction of nitrite to ammonium ion and hydroxylamine in buffered (pH 7) aqueous solutions. Controlled potential coulometry at potentials from −0.98 to −1.05 V vs Ag/AgCl in 4‐morpholinepropanesulfonic acid (MOPS) buffer yielded ammonium as the major product with Faradaic efficiencies ranging from 76–90 %. A foot‐of‐the‐wave analysis yielded calculated turn‐over frequencies of 61 s−1and 28 s−1 for the Ni and Co complexes, respectively. The Ni complex displayed a higher selectivity for NH4+/NH2OH than the Co analog. A computational examination of the catalytic mechanism of the Ni complex was used to support and elucidate the proposed chemical steps, provide some energetic details of the electron and proton transfers, and present a rationale for the selectivity of this reduction.

Electrocatalytic nitrite reduction to ammonia on an Rh single-atom catalyst

Electrocatalytic NO2− reduction to NH3 (NO2RR) holds great promise as a green method for high-efficiency NH3 production. Herein, an Rh single-atom catalyst where isolated Rh supported on defective BN nanosheets (Rh1/BN) is reported to exhibit the exceptional NO2RR activity and selectivity. Extensive experimental and theoretical studies unveil that the high NO2RR performance of Rh1/BN arises from the single-atom Rh sites, which not only promote the activation and hydrogenation of NO2−-to-NH3 process, but also hamper the undesired hydrogen evolution. Consequently, Rh1/BN assembled in a flow cell exhibits the highest NH3 yield rate of 2165.4 μmol h−1 cm−2 and FENH3 of 97.83 % at a high current density of 355.7 mA cm−2, ranking it the most efficient catalysts for NO2−-to-NH3 conversion.

Atomic tuning of 3D printed carbon surface chemistry for electrocatalytic nitrite oxidation and reduction to ammonia

A bifunctional electrode integrating 3D printed carbon materials with atomic layer deposition of TiO2 is developed for electrochemical nitrite oxidation and reduction, providing effective surface engineering for nitrite monitoring and remediation.

ZnFe2O4 nanosheet array: a highly efficient electrocatalyst for ambient ammonia production via nitrite reduction

ZnFe2O4 nanosheet arrays on nickel foam (ZnFe2O4/NF) act as a high-performance electrocatalyst for the electroreduction of NO2− to NH3.

Recent progress in the advanced strategies, rational design, and engineering of electrocatalysts for nitrate reduction toward ammonia.

Ammonia is a valuable feedstock for most chemicals, pharmaceuticals, and fertilizer products. It is a promising carbon-free energy source. Under severe experimental circumstances (high temperature and high pressure), ammonia is manufactured industrially using the standard Haber-Bosch process. This process uses a lot of energy and emits a huge amount of CO2 into the environment. One method that is seen to be promising and could eventually replace the Haber-Bosch process is the electrocatalytic production of ammonia. However, in ambient conditions, the cleavage of the nitrogen molecule is exceedingly difficult. As a result, the yield of ammonia remains modest and the study's scope is still restricted to the lab. When the catalytic performance is significantly increased, nitrate and nitrite contaminations in water systems can be effectively removed and simultaneously transformed into energy sources if nitrites or nitrates are employed as nitrogen sources instead of nitrogen gas. This may become a new substitute for the synthesis of ammonia, but nitrate and nitrite reduction are not getting enough attention. In this review, we discuss the performance of the electrocatalytic nitrate reduction reaction, which includes cycling stability, reactivity, selectivity, and faradaic efficiency. Following this summary, we look into the crucial elements, the rate-determining step, and the reaction mechanisms that govern the performance of the nitrate reduction reaction. In order to support the practical use of the electrocatalytic nitrate reduction reaction, we finally provided a summary of the challenges and future directions guiding the design of efficient catalyst and reaction systems.

Mechanistic studies of NOx reduction reactions involving copper complexes: encouragement of DFT calculations

Mechanistic analysis of nitrite (NO2−) and nitric oxide (NO) reduction reactions promoted by copper complexes provides a reliable view of electron transfer and atom movement.

Electrocatalytic reduction of nitrite to ammonia on undercoordinated Cu.

Electrocatalytic NO2--to-NH3 reduction (NO2RR) has emerged as an intriguing route for simultaneous mitigation of harmful nitrites and production of valuable NH3. Herein, we design for the first time undercoordinated Cu nanowires (u-Cu) as an efficient and selective NO2RR electrocatalyst, delivering the maximum NO2--to-NH3 faradaic efficiency of 94.7% and an ammonia production rate of 494.5 μmol h-1 cm-2 at -0.7 V vs. RHE. Theoretical calculations reveal that the created undercoordinated Cu sites on u-Cu can enhance NO2- adsorption, boost NO2--to-NH3 energetics and restrict competitive hydrogen evolution, thereby enabling the active and selective NO2RR.

A (μ-oxo) dicopper complex anchoring graphitized mesoporous carbon surface prepared by an in situ electrochemical method for bioinspired electrocatalytic reduction of nitrite to ammonia and sensing

The design and development of functional biomimetic systems that resemble natural enzymes is highly challenging.

Electrocatalytic reduction of nitrite to ammonium ion using Ni(ii) complexes with redox-active di(imino)pyridine ligands

Human disruption of the nitrogen cycle motivates the exploration into electrocatalytic reduction of nitrite.

Reduction of nitrite to nitric oxide and generation of reactive chalcogen species by mononuclear Fe(II) and Zn(II) complexes of thiolate and selenolate.

Comparative reactivity of a series of new Zn(II) and Fe(II) compounds, [(Py2ald)M(ER)] (E = S, R = Ph: M = Zn, 1aZn; M = Fe, 1aFe; E = S, R = 2,6-Me2-C6H3: M = Zn, 1bZn; M = Fe, 1bFe; E = Se, R = Ph: M = Zn, 2Zn; M = Fe, 2Fe), and [(Py2ald)M]22+ (M = Zn, 5Zn; M = Fe, 5Fe) is presented. Compound 1aZn could react with nitrite (NO2-) to produce [(Py2ald)Zn(ONO)] (3Zn), which, upon treatment with thiols and PhSeH (proton source), could regenerate either 1aZn/5Zn and2Znrespectively, along with the production of nitric oxide (NO) where the yield of NO increases in the order tBuSH ≪ PhCH2SH < PhSH < PhSeH. In contrast to this, 1aFe, 2Fe and 5Fe could affect the direct reduction of NO2- in the absence of protons to generate NO and [{(Py2ald)(ONO)Fe}2-μ2-O] (8Fe). Moreover, 8Fe could regenerate 5Fe and 1aFe/2Fe upon treatment with 4 and 6 equiv. of PhEH (E = S/Se), respectively, along with the generation of NO. Finally, a comparative study of the mononuclear Zn(II) and Fe(II) compounds for the transfer of the coordinated thiolate/selenolate and the generation and transfer of reactive sulfur/selenium species (RES-, E = Se, S) to a series of organic substrates has been provided.

Low-coordinated Pd metallene promotes the electrochemical reduction of nitrite to ammonia

A low-coordinated Pd metallene is verified to be an efficient catalyst for the NO2RR, which is attributed to the low-coordinated Pd sites to boost NO2− activation and reduce the energy barrier of NO2RR process.

Electrochemical reduction of nitrite to ammonia on amorphous MoO3 nanosheets.

Electrocatalytic NO2- reduction to NH3 (NO2RR) is an appealing approach for mitigating NO2- pollution and for the synthesis of valuable NH3, and so the exploration for high-performance NO2RR catalysts is pivotal yet remains challenging. Herein, amorphous MoO3 nanosheets (am-MoO3) were designed as a high-performance NO2RR electrocatalyst, delivering a maximum NO2--to-NH3 faradaic efficiency of 94.8% and NH3 yield rate of 480.4 μmol h-1 cm-2 at -0.6 V vs. RHE. Theoretical computations revealed that the largely enhanced NO2RR activity of am-MoO3 originated from the amorphization-induced O-vacancies, which could enhance the NO2--to-NH3 reaction energetics and hamper the competitive hydrogen evolution.

Co nanoparticle-decorated radix cynanchi daniculati-derived carbon for efficient electrocatalytic nitrite reduction to ammonia

As an efficient catalyst for NH3 production via NO2− reduction, Co nanoparticles decorated radix cynanchi paniculati-derived carbon exhibits a high faradaic efficiency of 92.77% with a NH3 yield of 1235.62 μmol h−1 cm−2 at −0.8 V.

Construction of Fe3O4@Au catalysts via the surface functional group effect of ferric oxide for efficient electrocatalytic nitrite reduction.

Surface modification is one of the effective strategies to control the morphology and electrocatalytic performance of noble metal/transition metal oxide matrix composite catalysts. In this work, we successfully introduced modification groups such as -NH2, -COOH, and -SH on the surface of Fe3O4 using the hydrothermal method. It was found that when the modification group -COOH was introduced, the regular spherical morphology of Fe3O4 was still maintained in Fe3O4-COOH, while Fe3O4-COOH had a relatively smaller spherical particle size (≈155.9 nm). Due to its smaller particle size, Fe3O4-COOH has a larger active area than Fe3O4, exposing more active sites. The abundant active sites in Fe3O4-COOH provide more nucleation and growth sites for Au particles, which is beneficial for the recombination between Fe3O4-COOH and Au. In addition, the experimental results of exploring the effect of Au precursor dosage on the synthesis of the Fe3O4-COOH@Au structure and performance show that the synthesized Fe3O4-COOH@Au1.0 catalyst has higher electrocatalytic activity. Due to the larger electrochemically active surface area of the Fe3O4-COOH@Au1.0 catalyst compared to those of Fe3O4-COOH@Au0.5 and Fe3O4-COOH@Au1.5 catalysts, the adsorption and activation of NO2- reactants were accelerated, thereby improving the electrocatalytic performance. Therefore, owing to the morphological and structural characteristics of Fe3O4-COOH combined with the high activity of Au nanoparticles, the synthesized Fe3O4-COOH@Au exhibits effective electrocatalytic activity in the electrocatalytic NO2-RR synthesis of ammonia. At a voltage of -0.8 V (vs. RHE), the ammonia yield reached 2092.8 μg h-1 mgcat-1 and Faraday efficiency reached 81.2%. The findings of this work will enrich our understanding of the construction of efficient Fe3O4@Au catalysts based on surface functionalization and help to design efficient electrocatalytic NO2-RR catalysts for practical applications.

Nitrous oxide production from biological and chemodenitrification by Fe(II) in estuarine and coastal sediments

Although biological processes are assumed the main sources of nitrous oxide (N2O), it has been increasingly highlighted that abiotic mechanisms are also at play. Here we investigated abiotic and biological N2O production from nitrate and nitrite reduction by Fe(II) in estuarine sediments through a series of anoxic incubations. N2O concentrations increased and then decreased with prolonged incubation time in biological treatment, which was attributed to biological reduction. N2O from chemodenitrification was not mediated by nitrate reduction, but instead was generated from nitrite reduction. Electrons transfer of Fe(II) oxidation decreased by 44.5% from abiotic to biological processes, reflecting that abiotic nitrite reduction was mainly responsible for Fe(II) oxidation. Pseudo-first-order rate constants of Fe(II) were higher in abiotic than biotic processes, and the constants of nitrite were higher in biotic than abiotic processes. 18ɛ:15ɛ ratios of nitrate and nitrite reduction were higher in abiotic than biological processes, suggesting that abiotic process represented a stronger oxygen isotope effect relative to nitrogen isotope effect than biological process. Site preference (SP) of N2O was higher in biological than abiotic processes and Fe(II) addition increased N2O production with accompanying high SP. Based on the reaction stoichiometry and electron transfer balance, chemodenitrification contributed to 20.2–38.4% of N2O production, and 61.6–79.8% of N2O was produced from biological denitrification. These result suggest that biological and chemodenitrification coupled with Fe(II) oxidation can produce N2O, which further mediate the kinetics of N2O production and have wide implications for coupled biogeochemical reactions between nitrogen and iron in global aquatic ecosystems.

The Abilities of Different Lactic Acid Bacterial Stains to Deplete Nitrite Level in MRS and M17 Broth

Nitrite is still regarded as essentially undesirable in foods. Therefore, it is necessary to keep its concentration under control for food safety. The current study was conducted to evaluate the ability of two reference lactic acid strains to deplete nitrite. Lactobacillus acidophilus ROO52 and Streptococcus thermophiles YC-180 were examined in De Man Rogosa and Sharpe (MRS) and M17 broth with standard sodium nitrite at 0.10 mg /mL and 1 mL (10-8 cells per mL) for each of the reference strains to determine the ability of these strains to eliminate nitrite during the fermentation period. A control group, MRS and M17 broth and standard nitrite without inoculum were used. The nitrite depletion was determined by a UV-Vis spectrophotometer. After 48 hours of fermentation, there were significant differences between residual nitrite levels of broth inoculated by Streptococcus thermophiles YC-180 compared to control and Lactobacillus acidophilus ROO52. Streptococcus thermophiles YC-180 depleted nitrite levels significantly (P˂0.05) from the initial concentration (0.10 mg/ml) to 0.02 mg/ml with a percentage (45%) after 48 hours compared to control and Lactobacillus acidophilus ROO52, which depleted nitrite levels from the initial concentration of 0.10 mg/ml to 0.04 mg/ml with a percentage (22.5%) after 48 hours. In conclusion, Streptococcus thermophiles YC-180 was more effective at nitrite depletion than Lactobacillus acidophilus ROO52. The reduction of nitrite occurs due to acid production and the enzymatic action of these bacteria.